The present invention relates to the making of thermally insulated tubes, and more particularly the invention relates to the making of tubing in which a longitudinally paid strip is folded about a tube which will become the inner tube, carrying spacers onto which an outer tubing is formed from the strip; the ring space between the two tubes is to be filled with foam.
Tubing of the type to which the invention pertains is made in the stated manner, using a continuously paid tube as inner tube upon which spacers are placed before a strip is formed around these parts and into the outer tube; the latter, being a split tube, is subsequently closed along the adjoining edges. However, a polymer, or polymer blend, which will foam under particular conditions, is placed into that ring space, just ahead of the continuous tube-closing operation such as welding, soldering, etc.
The spacers are provided to hold the inner tube in the outer one and to ensure a concentric disposition of the tubes to each other. These spacers are constructed, e.g., as disks (see German Pat. No. 1,779,406), or a helical spacer is wound around the inner tube (see, e.g., German printed patent application No. 1,960,932).
Disk-shaped spacers are very suitable, but their individual placement and positioning is a cumbersome procedure. The particular disk-shaped spacers of the German patent require a particular device for placement. Helical spacers are also very suitable, but the space to be filled with foam is rather restricted in most instances. Moreover, a helical spacer is to some extend an impediment for the spreading of the foaming substance. Consequently, cavities may form in the foam which are detrimental to the insulative properties and particularly with regard to the uniformity in the insulation. Also, it was found that a helical spacer interfers to some extend with the closing of the split tube. If the tube closing involves the application of heat, the spacer may suffer locally.